1. Field of the Invention
The present invention generally relates to a radio communication system and, in particular, to a radio communication control method and apparatus which corrects the oscillation frequency of a local oscillator for transmission and reception.
2. Description of the Related Art
In a radio communication system, a local oscillator is indispensable for frequency conversion, modulation, or demodulation and its accuracy is important to achieve reliable and stable receiving/transmitting control. As one of conventional methods, an automatic frequency controller using frequency correction data has been disclosed in Japanese Patent Unexamined Publication No. 3-70335. The frequency correction data is produced from the error between a receiving frequency and a reference frequency. The receiving frequency is obtained by a carrier recovery circuit.
According to the above conventional method, however, it is not ensured that the corrected oscillation frequency is precisely matched with the receiving frequency. In other words, there is a possibility that the receiving/transmitting control is performed using incorrect reference frequency. For this, there may be cases where reliable and stable control cannot be achieved.
Further, according to the above conventional method, the receiving frequency is acquired in a carrier recovery portion of a received burst signal and then the acquired frequency is held in a data portion of the received burst signal. Based on the held receiving frequency, the frequency correction is performed. However, the frequency correction cannot be performed with accuracy until the synchronization is established because the data portion cannot be determined until then. Furthermore, in cases where received data cannot be demodulated due to variations in reference frequency and thereby the synchronization is not acquired, the automatic frequency correction function itself fails to be performed.